The present invention relates to a friction material for use in brakes and etc. of cars and others, wherein, in particular, the noises generating on braking are prevented.
The conventional mechanical brake rubs solid members one another by contacting them, thus the noises generate inevitably due to the vibrations of them. Today, it is difficult to completely prevent such noises, and we are coping to decrease the noises by such methods that a material absorbing the vibration is formulated in one of opposing brake pads, that an elastomer with good viscoelastic characteristics is allowed to intervene on the way of vibration transfer system, and the like. However, it cannot still be said to be sufficient.
Here, the inventors have investigated the solution thereof and, paying an attention to the dust contained in the friction material of brake for following purposes, the investigations have been made further.
Namely, the main functions of organic dust are 1 improved brake feeling, 2 increased efficacy, 3 prevention of noises, and others. Types of dust include now rubber dust, cashew dust and modified articles thereof as shown in U.S. Pat. Nos. 4,310,452 and 4,886,107. The dusts are formed of particles of material of regulated size, after having vulcanized or cured the material of the dusts. The dusts are incorporated in an amount of 2-10 wt. % into the material from which disk brake pads are formed which include fiber reinforcing materials, inorganic fillers and thermosetting resin binder.
On the other hand, with respect to the environment surrounding the brake, the loading exerted on the brake pad is in a tendency to become increasingly severe, resulting from that the rigidity tends to decrease structurally from lightening in weight of car body accompanying with large-sized cars and that the brake system is also progressing toward miniaturization and lightening as well.
Hence, the requirement for the heat resistance of brake pad is increasing, but, with said rubber dust, the purpose is attained by no means and, with cashew dust, it has been difficult to effect the stabilized function over a long period of time, though the heat resistance thereof is higher than that of rubber dust. Namely, the noises generating with pad containing cashew dust have a strong tendency to generate more frequently as the braking is repeated. This is because of that, with increasing heat history due to the repetition of braking, the temperature of brake pad increases gradually and ends up to become over the heat decomposition temperature (about 290.degree. C.) of cashew dust at last, thus exceeding the heat-resistant limit of cashew dust.
As a result of further investigations in view of the points aforementioned, a friction material with excellent heat resistance having prevented the generation of noises has been developed according to the invention.